Liquid crystal materials are substances that exhibit some of the properties of solid crystals while in a liquid state over a particular temperature range that relate to its mesophasic state. Though liquid crystal materials have been known since at least 1889, it has only been recently that these materials have been used to create liquid crystal displays.
Liquid crystal displays are typically formed of flat panels of glass that are hermetically sealed with a layer of liquid crystal material between them. The inside surfaces of the glass plates each have a transparent conductive layer of material such as tin oxide sintered or baked onto the glass.
Though liquid crystals are comprised of three main types (smectic, nematic, and cholesteric), they are all characterized by molecules that are elongated and that are possessed of electrical dipole axes disposed at 90.degree. to the main axes of the molecules. When subjected to an electric field, the orientation of these molecules can be reordered.
In use, the conductive material disposed on the inner surface of the glass plates will be formed in the shape of the desired segment display, such as an alphanumeric character or portion thereof. Upon energizing the opposing conductive materials, the molecular contents of the liquid crystal material may be electrically rearranged. This will cause the material located between the opposing conductive surfaces to appear to the eye as a color or shade distinguishable from the main body of liquid crystal materials, which comprises the background color.
Many such displays are known in the prior art. These displays have found considerable use in applications where low power requirements are important, or where low voltage, low current and low surface temperature and characteristics are necessary for safety. To date, such displays are typically comprised of a single color for the background and a single differing color or shade for the display characters.
Some prior art users have obtained color displays by introducing an appropriate dye material into the liquid crystal material itself, or by the use of colored filters. No one has yet provided a liquid crystal display unit that can selectively display the segment characters in a variety of different colors against an opposing background.
Such a liquid crystal display unit could have many possible uses. In addition to being useful in meters or gauges where a particular condition could be highlighted by changing the color of the display characters, such an arrangement could be used for a solid state television screen. Therefore, it would be desirable to provide a multi-colored liquid crystal display device wherein the color of the segment display characters could be selectively changed.